1. Technical Field
The invention relates to a semiconductor substrate, a semiconductor device, a method of manufacturing a semiconductor substrate, and a method of manufacturing a semiconductor device, and is particularly suitable for application to a field effect transistor formed on an SOI (Silicon On Insulator) substrate.
2. Related Art
A field effect transistor formed on an SOI substrate has availability drawing attention in view of its easiness in element separation, latch-up free, small source-drain junction capacitance. In particular, since a complete depletion type SOI transistor can offer low power consumption and high operation speed and is easy to be driven with a low voltage, researches for making the SOI transistor in the complete depletion mode are actively conducted. Here, as the SOI substrate, for example, an SIMOX (Separation by Implanted Oxygen) substrate or a laminated substrate is used as disclosed in JP-A-2002-299591 or JP-A-2000-124092.
Further, JP-A-9-266170 discloses a method of forming an SOI structure on a bulk wafer. According to the method disclosed in the document, an oxide film is formed on a single crystal silicon substrate, and then an opening is provided in the oxide film to expose the single crystal silicon to form the base, and after then, an amorphous silicon layer is formed on the entire surface. And, the amorphous silicon layer on the oxide film is single-crystallized by the lateral solid-phase epitaxial growth using the single crystal silicon exposed through the opening as a seed crystal.
However, in order for manufacturing the SIMOX substrate, it is required to ion-implant oxygen to the silicon wafer in high concentration. Further, in order for manufacturing the laminated substrate, it is required to bond two silicon wafers with each other and then polish a surface of the silicon wafer. Therefore, the SOI transistors problematically incur higher cost in comparison with field effect transistors formed on bulk semiconductors.
Further, the ion-implantation process or the polishing process causes large variation in the thickness of the SOI layer. Therefore, if the SOI layer is made thinner for forming the complete depletion type of SOI transistor, it is problematically difficult to stabilize the characteristics of the field effect transistor.
Further, according to the method disclosed in JP-A-9-266170 described above, the amorphous silicon layer is single-crystallized while contacting the oxide film. Accordingly, the lateral single crystallization of the amorphous silicon layer is constricted by the oxide film to cause degradation of crystal quality of the single crystal semiconductor layer, and also it is problematically difficult to obtain a large sized single crystal semiconductor layer.